1. Field of the Invention
This invention relates to a method for characterizing contaminated soils and sediments so as to permit timely determination of the likely sources of rapidly released fractions of contaminants disposed in the contaminated soils and sediments, thereby enabling accurate decisions to be made as to the soils and sediments needing to be removed and/or treated to achieve risk-based cleanup objectives. The method is sufficiently rapid to enable decisions to be made in the course of excavating a contaminated site.
2. Description of Related Art
The characterization of contaminated industrial and governmental sites can involve significant costs due to the inability to define xe2x80x9csourcexe2x80x9d when used in describing sources of contaminants that significantly contribute to the degradation of groundwater, the inadequacy of current methods for measuring the fraction of contaminants that are available for transport to receptors such as groundwater, and the long lead times of days or weeks required for contaminant measurements to be obtained from commercial laboratories. These limitations prevent the timely definition of what constitutes a problematic source of contaminants at each site which would allow site managers to define which volumes of soil require aggressive treatment or removal and which soils are not an issue in terms of significant impact on receptors. Consequently, characterization costs of up to millions of dollars per site can be incurred without a true definition of source in terms of contaminant release rates, as a further result of which large volumes of soil are unnecessarily excavated and/or treated at substantial costs to the site owners.
Current methods for determining which volumes of soil are sources of contaminants and which soils are not range from the over-simplistic to the analytical approaches that require very long lead times of several days or weeks. One such method involves the determination of total concentrations of contaminants of concern. However, this type of data is of limited use in predicting the rates of contaminant release from various sections of the site. At such sites, decisions regarding cleanup levels and the planned removal and/or treatment of soil/NAPL (non-aqueous phase liquids) residues are guided by the total concentrations of the contaminants of concern. This results in a gross over-estimation of the volumes of soil/NAPL residues that are identified as xe2x80x9csourcexe2x80x9d for contaminants and that are subsequently targeted for aggressive management.
Other methods currently in use are visual observations of staining believed to be due to hydrocarbon impact and olfactory detection of contaminants through xe2x80x9chydrocarbonxe2x80x9d odor. However, visual and olfactory observations, as shown in Table 1 hereinbelow, are not good predictors of the potential of a soil/NAPL residue to impact groundwater or to become available to other receptors. Total concentration is also a poor indicator of contaminant availability to receptors.
It is, thus, apparent that there is a need for a method which provides reliable and rapid means for defining what soil/NAPL residues constitute significantly available sources of contaminants at contaminated sites.
It is, thus, one object of this invention to provide a method for defining soil/NAPL residues that constitute significantly available sources of contaminants at contaminated sites.
It is another object of this invention to provide a method for defining sources of contaminants in contaminated soils and sediments that significantly contribute to the degradation of groundwater and other contaminant receptors.
It is yet a further object of this invention to provide a method for measuring the fraction of contaminants in contaminated soils and sediments that are available for transport to receptors such as groundwater.
It is still a further object of this invention to provide a method for defining sources of contaminants in contaminated sites that reduces the amount of time required for obtaining such information in comparison to the days and weeks required by conventional methods.
It is yet a further object of this invention to provide a rapid method of estimating the mass of rapidly released hydrocarbon contaminants in each section of a site so as to quantify the spatial mass distribution of significant sources of rapidly released contaminants.
It is a further object of this invention to provide a method for defining sources of contaminants in contaminated sites that can be carried out at such contaminated sites.
These and other objects of this invention are addressed by a method for identifying and characterizing contaminated sources in a site comprising contaminated soils and sediments in which the vapor pressure at a plurality of subsurface soil sampling locations of the site is measured, producing a plurality of subsurface vapor pressure measurements with depth, which measurements are then mapped, resulting in generation of a subsurface vapor pressure map. The vapor pressure mapping indicates the spatial distribution of the total mass of rapidly releasable contaminants.
Commercially available instrumentation that provides contaminant-specific vapor pressures would yield a mapping of the rapidly releasable mass of only a specific contaminant. Concomittently, soil samples are analyzed in the laboratory for contaminant mobility using mobility test procedures such as the Synthetic Precipitation Leaching Procedure (SPLP), leaching tests and resin enhanced desorption of the soil. The results of these tests may be used to calibrate vapor pressure instrumentation. Using vapor pressure measurements together with total concentration measurements, contaminants in fast release compartments and slow release compartments in the contaminated soils and sediments are identified and the fraction of the contaminants in the fast release compartments and the slow release compartments rapidly determined in the field.